regcomp.c: Add conversion macros and use them

This adds macros that hide the details in finding the regnode address
from the offset from the beginning of the pattern's program, and vice
versa.

regcomp.c

@@ -883,6 +883,11 @@ static const scan_data_t zero_scan_data = {
                                        REPORT_LOCATION_ARGS(loc));      \
 } STMT_END
 
+/* Convert between a pointer to a node and its offset from the beginning of the
+ * program */
+#define REGNODE_p(offset)    (RExC_emit_start + (offset))
+#define REGNODE_OFFSET(node) ((node) - RExC_emit_start)
+
 /* Macros for recording node offsets.   20001227 mjd@plover.com
  * Nodes are numbered 1, 2, 3, 4.  Node #n's position is recorded in
  * element 2*n-1 of the array.  Element #2n holds the byte length node #n.
@@ -918,7 +923,7 @@ static const scan_data_t zero_scan_data = {
 } STMT_END
 
 #define Set_Node_Offset(node,byte) \
-    Set_Node_Offset_To_R((node)-RExC_emit_start, (byte)-RExC_start)
+    Set_Node_Offset_To_R(REGNODE_OFFSET(node), (byte)-RExC_start)
 #define Set_Cur_Node_Offset Set_Node_Offset(RExC_emit, RExC_parse)
 
 #define Set_Node_Length_To_R(node,len) STMT_START {			\
@@ -935,17 +940,17 @@ static const scan_data_t zero_scan_data = {
 } STMT_END
 
 #define Set_Node_Length(node,len) \
-    Set_Node_Length_To_R((node)-RExC_emit_start, len)
+    Set_Node_Length_To_R(REGNODE_OFFSET(node), len)
 #define Set_Node_Cur_Length(node, start)                \
     Set_Node_Length(node, RExC_parse - start)
 
 /* Get offsets and lengths */
-#define Node_Offset(n) (RExC_offsets[2*((n)-RExC_emit_start)-1])
-#define Node_Length(n) (RExC_offsets[2*((n)-RExC_emit_start)])
+#define Node_Offset(n) (RExC_offsets[2*(REGNODE_OFFSET(n))-1])
+#define Node_Length(n) (RExC_offsets[2*(REGNODE_OFFSET(n))])
 
 #define Set_Node_Offset_Length(node,offset,len) STMT_START {	\
-    Set_Node_Offset_To_R((node)-RExC_emit_start, (offset));	\
-    Set_Node_Length_To_R((node)-RExC_emit_start, (len));	\
+    Set_Node_Offset_To_R(REGNODE_OFFSET(node), (offset));	\
+    Set_Node_Length_To_R(REGNODE_OFFSET(node), (len));	\
 } STMT_END
 #endif
 
@@ -4555,7 +4560,7 @@ S_study_chunk(pTHX_ RExC_state_t *pRExC_state, regnode **scanp,
                             Perl_re_indentf( aTHX_  "%s %" UVuf ":%s\n",
                               depth+1,
                               "Looking for TRIE'able sequences. Tail node is ",
-                              (UV)(tail - RExC_emit_start),
+                              (UV) REGNODE_OFFSET(tail),
                               SvPV_nolen_const( RExC_mysv )
                             );
                         });
@@ -19302,13 +19307,13 @@ S_reginsert(pTHX_ RExC_state_t *pRExC_state, U8 op, regnode *operand, U32 depth)
                   "reginsert",
 		  __LINE__,
 		  PL_reg_name[op],
-                  (UV)(dst - RExC_emit_start) > RExC_offsets[0]
+                  (UV)(REGNODE_OFFSET(dst)) > RExC_offsets[0]
 		    ? "Overwriting end of array!\n" : "OK",
-                  (UV)(src - RExC_emit_start),
-                  (UV)(dst - RExC_emit_start),
+                  (UV)REGNODE_OFFSET(src),
+                  (UV)REGNODE_OFFSET(dst),
                   (UV)RExC_offsets[0]));
-	    Set_Node_Offset_To_R(dst-RExC_emit_start, Node_Offset(src));
-	    Set_Node_Length_To_R(dst-RExC_emit_start, Node_Length(src));
+	    Set_Node_Offset_To_R(REGNODE_OFFSET(dst), Node_Offset(src));
+	    Set_Node_Length_To_R(REGNODE_OFFSET(dst), Node_Length(src));
         }
 #endif
     }
@@ -19321,9 +19326,9 @@ S_reginsert(pTHX_ RExC_state_t *pRExC_state, U8 op, regnode *operand, U32 depth)
               "reginsert",
 	      __LINE__,
 	      PL_reg_name[op],
-              (UV)(place - RExC_emit_start) > RExC_offsets[0]
+              (UV)REGNODE_OFFSET(place) > RExC_offsets[0]
               ? "Overwriting end of array!\n" : "OK",
-              (UV)(place - RExC_emit_start),
+              (UV)REGNODE_OFFSET(place),
               (UV)(RExC_parse - RExC_start),
               (UV)RExC_offsets[0]));
 	Set_Node_Offset(place, RExC_parse);